1. Field of the Invention
The present invention relates to an electron multiplier and a photomultiplier tube each of which has an inverting dynode for inverting orbits of electrons which have passed through gaps provided in multi-anodes and for guiding the electrons back to the multi-anodes.
2. Description of Related Art
A multi-anode type photomultiplier tube provided with an inverting dynode has been proposed, for example, by Japanese Patent Unexamined Patent Application Publication (Kokai) No.6-314550.
FIG. 1 schematically shows a part of the multi-anode type photomultiplier tube of this publication. The photomultiplier tube includes a block-shaped dynode unit 100. The dynode unit 100 is constructed from a plurality of dynode plates which are stacked one on another. The plurality of dynode plates multiply electrons in a cascade manner. An anode unit 101 is located below the dynode unit 100. The anode unit 101 is constructed in a multi-anode structure. That is, the anode unit 101 includes a plurality of anodes 103, which are separated from one another by a plurality of electron passage gaps 102, through which electrons emitted from the dynode unit 100 pass.
An inverting dynode plate 104 is located below the anode unit 101. The inverting dynode plate 104 is formed with a plurality of electron incident portions 106. The electron incident portions 106 are provided in one-to-one correspondence with the anodes 103. That is, each electron incident portion 106 is located confronting an electron passage gap 102 that is positioned to the left of a corresponding anode 103. Each electron incident portion 106 has an upper flat surface 105 for receiving electrons which have passed through its confronting electron passage gap 102, for generating secondary electrons, and then for invertedly guiding the secondary electrons to the corresponding anode 103.